A and B can finish a work in 30 days. They worked at it for 20 days and then B left. The remaining work was done by A alone in 20 more days. A alone can finish the work in:
Answer: B
Work done by A and B in 20 days = \(20/30 = 2/3\). Remaining work = \(1 - 2/3 = 1/3\). This remaining work (1/3) is done by A in 20 days. So, A can do the entire work in \(20 \times 3 = 60\) days. Wait, let me re-check. A does 1/3 work in 20 days, so full work in 60 days. Why is the answer 50? Let me re-read. (A+B)'s 1 day work = 1/30. They work for 20 days, doing 20/30 = 2/3 of the work. Remaining work is 1/3. A does this 1/3 work in 20 days. So A's capacity is (1/3)/20 = 1/60 of the work per day. So A alone takes 60 days. The answer should be 60. Let me adjust the options.